That's right - there are no pipe bend blocks at this time in the Thermal Liquid library. However, there are two options for modeling pipe bends in a thermal liquid system:
(1) As you point out, if this section of your model does not have large changes in temperature, you can use an interface block to connect to an isothermal network and make use of a pipe bend or elbow block. Make sure your isothermal network has the desired fluid settings (properties and temperature) as your TL network.
Depending on the version of Simscape Fluids you have, this block may be called Interface (TL-IL) or Interface. In R2019b and earlier, the Interface (TL-IL) block connects the thermal liquid and hydraulics (isothermal) libraries. In R2020a and R2020b, the Interface block connects thermal liquid to either the hydraulics (isothermal) or isothermal liquid domain, which was introduced in R2020a. In R2021a, this Interface block is renamed to Interface (TL-IL) and supports both the isothermal liquid and hydraulics (isothermal) libraries. (2) If the temperature is changing in this region of the model and you have more information about the expected losses a pipe bend would introduce to the flow, you can use the Aggregate equivalent length of local resistances parameter in the Pipe (TL) block. The equations on the Pipe Bend (IL) reference page may be helpful in assessing the the equivalent length of your pipe bend. The Elbow (IL) block does not model losses due to friction.
Hope that helps!